Wave signaling system



Nov. 15, 1927.

1,649,589; A L. A. HAZELTINE WAVE S IGNALING SYSTEM Original Filed Feb. 27, 1925 2 Sheets-Sheet l (M INVENTOR, o0/5 JazeZzme ATTORN EY Nov. l5, 1927. 1,649,589

L. A. HAZELTINE WAVE S IGNALING SYSTEM originalFiled Feb. 2'?, 1925 2 sheets-sheet 2 INVENTOR,

L' 0 wfs A', Hazelfme ATTORNEY S Patented Nov. -15, 1927. i

UNITED STATES PATENT OFFICE.

LOUIS ALAN HAZELTINE, OF HOBOIKEN, NEW JERSEY, ASSIGNOR TO HAZELTINE COR- PORATION, A CORPORATION 0F DELAWARE.

WAVE SIGNALING SYSTEM.

Original application formers so that their input conductances are related in a certainway to the conductances of the vacuum tubes. The manner in which the conductances are related and the advantages thereof are more fully explained in my co-pending U. S. application entitled Wave signaling systems, Serial No. 12,000, led February 27, 1925, of which the present application is a division.

Theeliminationl of coupling betweenv the plate circuits and grid circuits of the vacuum tubes is accomplished by the cooperation of three steps: First, the arrangement of the amplifier transformers so that there is substantially no magnetic coupling be-` tween any two of them; second, the avoidance in the wiring of any substantial impedance common to two or more tunedcircuits; and third, the neutralization of natural capacity couplinginherent between the tuned circuits including, particularly, that due to the capacity between the grid and plate ,of the vacuum tube.

The elimination of undesirable Vcoupling between the plate and grid circuits results in the prevention of feed-back or regenerative action, .and consequently there 1s no tendency. towards the production of local oscillations. The neutralization of such unj desiredl capacity coupling is in general explained in my U. S. Patents Nos. 1,489,228 and 1,533,858. A d

The particular object of the present invention is the provision ofL suitable and readily available means for the reduction of the undesirable effects lof capacity coupling between circuits of oie or more of the vacuum tubes, whichy may or may not be connected adjacently, by arranging appara`- vtus in an'input circuit and apparatus" in' a led February 27, 1.925, Serial No. 12,000, and in CanadaV May 4, 1925; Divided and. this application led September 24, 1927. Serial No. 221,647.

succeeding input circuit or output circuit so as to have natural capacity therebetween,

and adjusting the natural capacity to attain at least partial neutralization of such undesired'capacity coupling. To produce satisfactory results by itself, this partial neutralization should at least be suiicient to prevent undesired oscillations due to the capacity coupling. In order to effect such neutralization, it is necessary that the polarity of certain points in the input and output circuits bear the proper relation to each other,

as will hereinafter be explained in connection with the drawings.

Referring to the drawings:

Figures 1a and 1b show a plan and an elevation, respectively, of a tuned radio-frequency amplifier to which this invention has been advantageously applied.

Figure 1c shows the diagram of connections of the receiver. of Figures 1a and 1b.

Figure 1d shows the structure of the radiofrequency amplifier transformers of Figures 1a and l".

Figure 1e shows a modification of the circuit of Figure 1c.

lFigure 2 shows the connections of a radio receiver embodying this inventionand employing natural inherent capacity for the neutralization of the capacity coupling effectively existing between the input and output circuits of a vacuum tube, with certain novel means forv adjusting the neutralizing capacity.

In the yradio receiver represented in Figures 1 and 1b there are three radio-frequency transformers Ta, T1, T2, each associated with a tuning condenser Ca, C1, C2. Each coil is-mounted on the back of its condenser for the purpose of 'keeping as short as possible the leads between them and for other purpose, as disclosed in my U. S. Letters Patent No. .1,577,421 and in my co-pending application` Serial No.. 40,488,

filed Junev 30, 1925. The vacuum tubes are mounted adjacent to the coils and condensers with which they are associated, also in order. to keep the connecting leads as short as possible. The coi/ls of each transformer are preferably of the single-layer type, as illustrated in Figure l, and are mounted with axes parallel and at an angle of substantially 55 degrees with the line of centers, this being a convenient arrangement resulting in zero magnetic coupling between any two of the transformers, as described in my patent and co-pending application just referred to. Careis also taken to avoid magnetic coupling between stages that might be due to closed conducting loops linked with the fields of two or more transformers. Such loops might exist in a supporting metal framework, or in the leads from the batteries which leads are therefore preferably hunched together.

Figure l shows the diagram of connections for the receiver of Figures lEL and l". The reflex principle is employed by which radio-frequency amplifying tubes A1 and A, serve also as audio-frequency amplifying tubes through the use of two audio-frequency transformers T., and Tm. The jacks JD, J1, J2 enable ahead telephone receiver, or loud speaker, to be plugged in the plate eircuit of the detector tube or either of the audio-frequency amplifier tubes. v

Since each coil of an audio-frequency transformer has la high impedance to radio#A frequency current, by-pass condensers Cm, C82, CP1, CP2, Cpd are arranged to provide lowJ impedance return paths for the radio-frequency grid and plate currents direct Ito the respective filaments. `This keeps radio-frequency currents out of the common battery leads, which may have sufficient reactive impedance as to cause objectionable coupling if they carry radio-frequency currents of different stages. The grid by-pass capacities C81, Cg2 may be of theorder of one tenthousandtlis microfarad, and the plate bypass capacities Cm, CP2, Cpd may be of the order of one one-thousandths microfarad, these values giving low radio-frequency impedances, but sufficiently high audio-frequency impedances' notto shunt unduly the audiofrequency transformer coils 'and so lower the audio-frequency amplification.. The leads to the by-pass condensers should be short to minimize their reactive impedances.

In case the radio-frequency current in the plate circuit of detector tube D passes in appreciable amount through the primary of Ta1 and so couples tube D with tube A1, then aradio-frequency impedance Lp, (Figure le) may be inserted in the lead from the plate of tube D, and a condenser Cpd may e connected directly from this plate to the filament.` Care must be taken that the im'- pedance coil Lpd is not coupled magnetically to any of the radio-frequency transformers.

The filament system should be grounded,

referably at X, Figure 1, so that radiorequency current passing from the antenna through the natural capacity between the coils of TaL will flow directly to ground, and not through thebattery leads to the other tuned circuits and thence through their natural capacities to ground, which would result 1n undesirable coupling betweeny the stagess Coupling between the plate circuit and the grid circuit of tube A1, due to the natural capacity Cc, between the grid with its connected apparatus and the plate with its connected apparatus, is neutralized by the ncutralizing capacity Cn, connected between the grid and the auxiliary coil ab, which in Figure lc is a portion of the secondary coil a0 of the transformer T1. As explained in my U. S. Letters Patent N o. 1,489,228, neutralization will be effected when the primary coil de and the auxiliary coil a?) are closely coupled electromagnetically and have terminals a and c, which connect to the filament system, of opposite polarity, and when the ratio of the number of turns of ab to the number of turns of (le is equal to the ratio of Cc1 to CD1. The saine arrangement and relation applies, of course, to the neutralizing capacity Cn, and the output transformer T2, associated with the second amplifier tube A2.

Figure 1d shows the'construction of the transformers T1 and T2. The primary winding de is ymounted so as to have close magnetic coupling to the tapped portion ab of the secondary coil ac, the tap b connecting to the neutralizing condenser CD1 or Cng, as shown in Figure 1. To make the coupling as close as possible between the auxiliary coil ab and the radio-frequency plate circuit, the leads from d and e and the leads to the plate by-pass condenser CI,1 or Cm, Figure 1, should be made as short as possible. Such closeness of coupling is needed because the radio-frequency current flowing conductively through the plate of the vacuum tube would build up an appreciable voltage in the leakage reactance of the plate circuit, which voltage would not be balanced by a voltage in the auxiliary coil ab. The pri mary and secondary coils in Figure l" are wound in the same direction, with the result that terminal a connecting to the filament system, Figure l, is of opposite polarity to terminal e also connected to the filament system, (or, in other words, the low-potential terminals a and e are of opposite polarity, and the same is therefore true of the highpotential terminals o and al), as required for the purpose of neutralization. The connection of the neutralizing` condenser to a tap b, so that ab is a small portion of the secondary winding, allows close coupling to be obtained between ab and le and at the same time requires the primary winding (le to extend under only asmall portion of the secondary, thus minimizing natural capacity and dielectric loss due to the dielectric field between primary and secondary. The primary winding, as indicated, is placed adja cent to the filament end a of the secondary winding,` for the same purpose.

In general, there will exist natural capacity between the apparatus connected to the llfl in, as heard on a telephone receiver plugged grid of A1 and apparatus connected to the grid of A2. Such natural capacity has a neutralizing tendency and so,D in part, supplants CD1. This neutralizing capacity is relatively more effective, for a given value, as the ratio of turns of a@ to de is greater than that of ab to de. On account of the difficulty of accurately measuring or calculating very small capacities, particularly natural capacities, the proper neutralizing capacities Cn1 and Cu2, Figure 1c, are in practice determined by trial. A suggested procedure for neutralizing is as follows: First with the filament of A2 cold, and those o A,L and D lighted, a strong signal is tuned in the detector plate circuit; 02 is then adjusted until the signal disappears, showing that no coupling exists between the plate circuit and the grid circuit 'of A2. Then with the filaments of D and A2 lighted and giet of A1 cold, the process is repeated with On account of the proximity of the radiofrequency transformers to one another and more especially of the presence of a loop formed by the leads between each secondary and its tuning'condenser, the actual coil'inclination for zero magnetic coupling may differ slightly, but appreciably, from its theoretical value of substantially 55 degrees. Hence, the proper inclination must also be determined by trial, and may be in accordance with the following procedure: With all coils at the same inclination, Cn, and Cn2 are adjusted for zero coupling as described in the preceding-paragraph, with the circuits Y tuned i'irst for a low frequency and then for a high frequency. In general, the settingsl found for the two frequencies will be dif- Y ferent, showingthat the capacity coupling,

which varies with the frequency, 1s being called upon to compensate for some magnetic coupling. The coil inclinations are then varied together, until the settings of C, and (3,12 are found to be theV saine at the two extreme frequencies.

TheA determination of the proper coil angle need ordinarily be made only once for a given design of receiver, but the adjustments of the neutralizing capacities are made in each individual receiver.

The transformer Ta preferably has a like secondary coil to T1 and T2, but its primary coil\ usually should have more turns, especially ifthe antenna to be employed is of small capacity and resistance. With a considerable step-up ratio, the capacity and the resistance of the antenna are equivalent to much smaller. capacity and resistance in the secondary circuit.

With the Aantenna polarity indicated by Ta, Figure 1, adjacent turns of primary and secondary are at the same` radio-frequency potential, soV there is no dielectric field be-f tween primary and secondary as there is 1n T1 and T2. Hence Ta has less natural capacity than T1 and T2, which tends to compensate for the capacity added by theantenna. The three condensers being alike, the three tuning dials represented in Figure lb will thus read nearl alike when all are adjusted to any one frequency. This greatly simplifies the process of tuning the receiver. The result just described, i. e., thatall tuning dials will read substantially alike when in proper adjustment` for reception, is of course dependent upon the absence of regenerative action, and contrasts with prior receivers employing tuned radio-frequency amplification without the elimination of undesirable coupling between stages; for in such receivers detuning of the amplifier output circuits was ordinarily necessary for the control of regeneration and oscillation, and in any case the tuning adjustment was dependent upon the regeneration present and Dtherefore upon the state of the batteries and of the vacuum tubes Figure 2 illustrates a two-tube radio receiver in which the tube A1 is used both as a radio-frequency and an audio-frequency amplifier. 1n the receiving apparatus illustrated by this ligure, neutralization of capacity coupling between the input and output circuits of tube A1 is attained through utilization of the natural capacity Cu existing between the apparatus connected to the grid of tube A1 and the grid of tube D respectively. This natural capacity may readily be made too large by mounting the two variable condensers Ca and C, close together. An adjustable grounded metallic shield S may then be introduced between these two condensers and moved until neutralization is attained. Such neutralization could likewise be effected by the capacity between the tuning condensers of several radio-frequency stages. As pointedout in my United States Letters Patent first above-mentioned, neutralization will obtain when the value of the effective grid-platel capacity of tube A1 divided by the value of capacity represented by Cn is numerically equal to the number-of turns of coil Ls1 divided by the number of turns of the coil Lm, provided the value of coupling between L,1 and Ls1 be sufficient.

It is also essential that the relative polarities of the coils Lp1 and L,s1 be arranged in accordance with the description given in my United States patents and pending applications previously mentioned, and to that end it is necessary in the present instance that the high-potential terminal of the primary coil L1 be of opposite polarity to the high-potential terminal of the secondary coil LS1. As previously suggested, it is possible Ito arrange portions of apparatus other than the variable condensers referred to with suiciently close electrostatic relation to atlila tain the degree of neutralization desired: for example, the input and output transformers associated with the tube A,L and having secondary coils Ls and L.,1 respectively may be so al'ranged as to include the required neutralizing capacity between their windings; or both together may be used.

It is to be understood that in the receiver represented by the circuit diagram of Fig ure 2, the-radio-frequency transformers employed to couple the antenna to the first radio-frequency amplifier stage and also the transformers employed to couple successive tubes are to be arranged in such a manner as to eliminate as far as possible all magnetic coupling between the different transformers. Such electromagnetic isolation may be achieved through the use of electromagnetic shielding as described and illustrated in the patent specifications first referred to, or by mounting the transformers with their axes parallel and at an angle of substantially to the common' line of centers of the coils, as described in my U. S.' Letters Patent No. 1,577 ,421 previously mentioned.

I claim: l

1. In aradio-frequency amplifier including a vacuum tube having an input circuit and an output circuit, said circuits being undesirably coupled by capacity, apparatus including a coil in said input circuit and apparatus includinga-transformer in said output circuit, the method of reducing the undesirable capacity coupling between said input and output circuits which comprises arranging the high-potential terminal of the primary coil of said transformer to beof opposite polarityto the high-potential terminal of a secondary coil thereof, placing a portion of the apparatus connected to said secondary coil'so as to have naturalcapacity to a portion of the apparatus connected to the coiiin said input circuit, interposing an electrostatic shield between said portions of apparatus, and adjusting the position of said shield, whereby said undesirable capacity coupling is atleast partially neutralized.

2. A radio-frequency amplifier including a vacuum tube having a filament system, an input circuit and an output circuit, said circuits being undesirably coupled by capacity, apparatus including a coil in said input circuit, and apparatus including a transformer in said output circuit, portions of said apparatus being in electrostatic relation to each other, the high-potential terminal of the primary coil of said transformer being of opposite polarity to the high-potential ter-- `shield maintained substantially at the alternating-current potential of said filament system, said shield being adjustably interposed between said portions of apparatus wherewith to effect adjustment of said neutralization.

3. In a tuned radio-frequency amplifier i 4circuit and an output circuit, said circuits being undesirably coupled by capacity, a coil and a variable tuning condenser in said input circuit, a transformer in said output circuit, and a variable condenser connected across a secondary coil thereof for tuning the same, the method of reducing the undesirable capacity coupling between said input and output circuits which comprises arrang ing the high-potential terminal of the primary coil of said transformer to be of opposite polarity to the high-potential terminal of said secondary coil thereof, placing said tuning condensers in electrostatic relation to each other, interposing an electrostatic shield between said condensers, and adjusting the position of said shield whereby to effectat least partial neutralization of said undesirable capacity cou line.

4. A tuned ra io-farequency amplifier including a yacuum' tube having a filament system, an input circuit and an output circuit, said circuits being undesirably coupled by capacity, a coil and a variable tuning condenser in said input circuit, a transformer in said' output circuit, and a variable condenser connected across a secondary coil of said transformer for tuning the same, the highpotential terminal of the primary coil of said transformer being of opposite polarity to the high-potential terminal of said secondary coil thereof, said tuning condensers being in electrostatic relation to each other,

whereby at least partial neutralization of said undesirable capacity coupling is obtained, and an electrostatic shield maintained substantially .at the alternatingcurrent potential of said filament system, Said shield being adjustably interposed between saidcondensers wherewith to effect adjustment of said neutralization.

Inwitness whereof, I aix my signature.

LOUIS ALAN HAZELTIN'E. 

